The present invention relates to hydraulic pumps, although other uses will be apparent from the teachings disclosed herein. In particular, the present invention relates to Bantam Duty Pumps (BDP) which can be combined with motors and other remotely-located units. When used in this manner, these BDP units provide an infinitely variable flow rate between zero and maximum in both forward and reverse modes of operation.
Pumps discussed herein are of the axial piston design which utilize spherical-nosed pistons, although variations within the spirit of this invention will be apparent to those with skill in the art and the invention should not be read as being limited to such pumps. One such prior art pump is shown in FIG. 1. The pump is a variable displacement pump 10 designed for vehicle applications. A compression spring 12 located inside each piston 14 holds the nose 16 of the piston 14 against a thrust-bearing 18. A plurality of such pistons positioned about the center of the cylinder 20 forms a cylinder block kit 22. The variable displacement pump 10 features a cradle mounted swashplate 24 with direct-proportional displacement control. Tilt of swashplate 24 causes oil to flow from pump 10; reversing the direction of tilt of the swashplate 24 reverses the flow of oil from the pump 10. The pump is fluidly connected with a motor to form a pump-motor circuit having a high pressure side and a low pressure side through which the oil flows. See generally FIG. 4C. Controlling the oil flow direction, i.e. changing the high and low pressure sides, controls the motor output rotation. Tilt of the swashplate 24 is controlled through operation of a swashplate control shaft 26 (also referred to herein as trunnion arm). The trunnion arm is connected to a slide which connects with the swashplate. Generally, movement of the trunnion arm 26 produces a proportional swashplate movement and change in pump flow and/or direction. This direct-proportional displacement control (DPC) provides a simple method of control.
A fixed displacement gerotor charge pump 28 is generally provided in BDP units. Oil from an external reservoir (such as reservoir 200 in FIG. 4C) and filter is pumped into the low pressure side by the charge pump 28. Fluid not required to replenish the closed loop flows either into the pump housing 30 through a cooling orifice or back to the charge pump 28 inlet through the charge pressure relief valve. Charge check valves 32 are included in the pump 10 and end cap 34 (cap 34) to control the makeup of oil flow of the system. A screw type bypass valve 36 is utilized in the pump 10 to permit movement of the machine (tractor, vehicle, etc.) and allow the machine to be pushed or towed. Opening a passage way between fluid ports with bypass valve 36 allows oil to flow, thereby opening the pump-motor circuit, which allows the motor to turn with little resistance because the vehicle wheels will not back drive pump 10.
While such pumps are useful, they have the disadvantage of having a preferred alignment direction. More particularly, the housing 30 has a preferred alignment with the end cap. This preferred alignment direction is created by the hose coupling, or connections, between the motor 38 and the pump end cap 34 (see FIGS. 2 and 3). The placement of the system ports 40 determines the preferred alignment of the housing 30. This is particularly troublesome when one desires to control a hydraulically powered vehicle with pumps positioned on either side of the vehicle and where the control arms for the individual pumps also must be mounted to the outer sides thereof. A control arm for the left pump 10L (FIG. 2), for instance, can be conveniently connected to the trunnion arm 26 to provide control of the swashplate from the left. However, to connect a control arm to the right pump 10R, for instance, the pump must be rotated to place the trunnion arm 26 nearer to the right side of the vehicle. Costly hose fittings are then required to connect the hoses 44 to the pump 10R. Alternatively a cumbersome and costly U-shaped control linkage 46 may be connected to the trunnion arm 26 while maintaining the pump end cap in its preferred orientation, as shown in FIG. 3.
An improvement on the earlier pumps having preferred alignment is shown in FIG. 4C; the corresponding end cap 156 is shown in FIG. 14A. FIGS. 4C and 14A disclose a prior art pump wherein the end cap 156 may be connected to the housing in one of two orientations. Specifically, end cap 156 is rotatable 180xc2x0 with respect to the housing. This permits the trunnion arm 26 to be placed on opposing sides. This improved xe2x80x9csymmetric pumpxe2x80x9d has shortcomings, however, which the present invention overcomes. The advantages of a symmetric pump according to the present invention over the prior art xe2x80x9csymmetric pumpxe2x80x9d will be apparent to those with skill in the art from the teachings herein.
The present invention overcomes these and other problems by providing a pump which does not have a preferred mounting alignment. One object of the present invention is to provide a new and improved pump. A further object is to provide a symmetric pump having a symmetric housing and a symmetric end cap.
Another object of the present invention is to provide an improved hydrostatic vehicle.
Another object of the present invention is to provide means for utilizing a hydraulic pump in multiple directions without the cost of expensive fittings and accessories.
Accordingly, the present invention includes a pump having a housing and an end cap. The housing includes a pump shaft rotatably supported therein. The end cap may be connected to the housing in either a first position or a second position rotated relative to the housing from the first position about an axis through the pump shaft.
Another embodiment of the invention includes a pump comprising an end cap and a housing connectible to the end cap in either a first position relative to the end cap or a second position rotated relative to the first position. The second position is rotated relative to the end cap (and the first position) about an axis through the housing and the end cap. The housing is connected to the end cap in one of the first or second positions.
Another embodiment of the invention includes a pump comprising a housing and a swashplate rotatably supported in the housing. A pump shaft is supported by the housing and extends through the swashplate. A trunnion arm is extended from the housing and positioned to vary or act upon the operation of the swashplate. An end cap is connected to the housing. The end cap has a system port opening external thereto in a first orientation. The pump further comprises connection means for connecting the housing to the end cap in one of a first position and a second position such that the trunnion arm extends in a first direction and the system port opens in the first orientation when the housing is connected to the end cap in the first position. The connection means also provides connection such that the trunnion arm extends in a second direction and the system port opens in the first orientation when the housing is connected to the end cap in the second position.
The invention includes an end cap for a hydraulic pump, wherein the pump includes a housing adapted to connect to the end cap.
The end cap comprises a first edge and a second edge separated by a third edge. A first check plug and a first case drain are positioned in the first edge. A second check plug and a second case drain are positioned in the second edge. A pair of system ports are positioned in the third edge.
The invention also provides a control device for a hydraulic pump having a housing and a swashplate operably supported therein and a trunnion arm engaging the swashplate. The control device comprises a control arm attached to the trunnion arm and a stud mounted in and extending from the housing a spaced distance from the trunnion arm. The stud is positioned parallel to the trunnion arm. Structure is attached to the stud and engages the control arm to restrict rotation of the control arm.
A symmetric pump comprising structure to restrict movement of the control arm is also provided. The present invention also provides a method of securing a swashplate in a neutral position for shipment and attachment to a vehicle.
Other objects and advantages of the present invention will be apparent from the following detailed discussion of exemplary embodiments with reference to the attached drawings and claims.